We are investigating the effects of acetylcholine antagonists and agonists on the activity of ganglion cells in the rabbit retina. The rabbit retina contains ganglion cells with centre-surround receptive fields, which can be categorized as X, Y, sluggish sustained and sluggish transient, as in the cat. In addition, some are color coded, and some have more complex receptive fields (directionally selective, orientation selective, local edge detection, uniformity detection, large field units). We will test the effects of mecamylamine, dihydro beta-erythrodine, choline, arecoline, nicotine, hexamethonium, atropine, and other agents on all types of receptive field. The purpose is to determine whether the synaptic transmitter acetylcholine contributes to the activity of some ganglion cells but not others, and whether, for the cells that are affected, a particular aspect of the receptive field is altered.